The present invention relates to the field of the treatment of the exhaust gases of a motor vehicle internal combustion engine, and more particularly, a method and a device for detecting the presence of an exhaust gas treatment system in an exhaust line of a motor vehicle.
The invention applies to all types of treatment systems: particulate filter type, nitrogen oxide trap, catalytic or oxidizing converter, etc.
Some current regulations require that on-board diagnostic systems, which check that exhaust gas treatment devices are operating correctly, be responsible moreover for detecting the presence of such a system.
Various types of technique are currently used to detect the presence or the absence of an exhaust gas treatment system in an exhaust line.
Thus, detecting the presence of a particulate filter in an exhaust line of an internal combustion engine using a determination of the differential pressure at the boundaries of the filter is known, the absence of the particulate filter being shown by a change in behavior of the differential pressure.
However, this technique requires working at high volume flow rates. Moreover, the signals supplied are not very reliable, because the differential pressure is usually worked out from very noisy measurements.
Detecting the presence of a nitrogen oxide trap is also known using signals supplied by an exhaust gas mixture sensor placed downstream of the filter, such as a binary mixture sensor, or a proportional mixture sensor, the mixture composition detected making it possible to determine the absence or the presence of the nitrogen oxide trap in the exhaust line.
This technique also has a certain number of disadvantages relating in particular to the fact that the signals supplied by the sensor are not very reliable, because the aging of the sensor causes a shift in the measurements provided, and relating to the cost of the sensor. Moreover, the mixture composition measured by the sensor must be processed in relation to the mixture composition of the exhaust gases upstream of the nitrogen oxide trap. Now, with regard to diesel engines, it is difficult to check the mixture composition of the exhaust gases upstream of the nitrogen oxide trap, so that this technique is relatively difficult to employ reliably.